Solar modules are devices for conversion of sun light into electrical energy and comprise a one-dimensional array or a two-dimensional array of individual solar cells, for example an array of 1×10, 6×12 or 8×12 solar cells. The overall size of a solar module is for example 0.8×1.6 m or 1×1.6 m.
Silicon based solar cells comprise silicon single crystal cells (“solar silicon wafers”), poly crystalline silicon cells and amorphous silicon cells.
Such solar cells (2) are mounted onto a support substrate (5) such as a sandwich of a glass plate (6) and an encapsulant (7) such as a foil of ethylvinylacetate (EVA) or a silicone sheet which faces the sunlight during use of the solar module (1). Horizontal spacings (3) between individual solar cells (2) are present. The corresponding P-type and N-type diffusion regions of individual solar cells are electrically contacted by attaching wires, clamps or a combination thereof (4) on and between solar cells (2) (FIG. 1).
Different strategies are known for electrically contacting solar cells with each other: solar cells (2) already having attached a wiring portion to one or both sides are mounted onto the support substrate (5) and wires and/or clamps (4) are soldered or glued onto contact areas (8) on the solar cells (2) bridging the horizontal spacing (3) between two solar cells (2) attached to the substrate of a solar module (1). A method for connecting solar cells by clamps (4) is disclosed in US 2012/0160294 A1. The mechanical stability of wires and/or clamps (4) soldered onto contact areas of two silicon cells and bridging the horizontal spacing (3) between said two solar cells attached to a support substrate (5) is not always sufficient.
This is for example shown in FIG. 2: in case the at least two solar cells (2) and (2′) are mounted on top of the encapsulant (7) (FIG. 2a) or are partially embedded into the encapsulant (7) (FIG. 2b), a height difference (9) between the surface of the at least two solar cells (2) and (2′) opposite to the support substrate (5) and the encapsulant (7) results. The wiring and/or clamping (4) between two solar cells (2) and (2′) is bended in the region between the edge of a solar cell (2) and (2′) and the surface of the encapsulant (7) in order to mechanically support said wiring (4) (FIG. 2c). The bended wiring portion (10) has an increased internal stress and accordingly a decreased reliability in later use of the solar module (1) where for example large temperature differences of e.g. 50° C. promote formation of cracks (11) in the bended wiring portion (10) (FIG. 2d).
Furthermore, solder joints or joints between a solar cell (1) and the wiring and/or clamping (4) formed by an (electrically conductive) adhesive are also a source of malfunction of the solar module (1) during manufacture or later use of the solar module (1).
Document GB 1 553 025 A discloses a method for manufacture of a wiring on individual solar cells wherein grooves are formed in a silicon wafer and successively filled with aluminium. Said aluminium wiring is in direct contact with the side walls of the grooves formed in the silicon wafer. Accordingly, such an method is not applicable to the formation of a copper and/or copper alloy wiring between individual silicon solar cells because silicon and copper diffuse into each other and thereby the intrinsic properties of solar silicon material is altered in an unacceptable manner.
Document WO 2006/093023 A1 discloses a dual damascene plating method for the manufacture of microchips from individual silicon wafers.
Document EP 0 710 991 A1 discloses a method for connecting a group of solar cell elements with metal foil members on the back faces of the plurality of the solar cell elements arranged next to each other.